The invention relates to a device for diverting individual items from a stream of items which are conveyed on a transport apparatus. The device contains an extendable and retractable diversion element which is precisely time-controllable in order to impart a cross impulse to the items to be diverted so that they slide from the transport apparatus across the direction of transport. The diversion element is operated via a gear unit by a drive apparatus moving or swinging to and fro, e.g. by a piston-cylinder unit or a stepped motor oscillating to and fro.
Such diversion devices are used e.g. for sorting out defective drinks bottles or other empty or already-filled food containers or packages. The transport apparatuses are conveyor belts, link chain conveyors or similar, two or more such conveyors running parallel to one another and the diversion device being intended to move the defective bottles or containers from a first conveyor to the conveyor or one of the conveyors running alongside.
Diversion devices with a striker which is operated by a pneumatic cylinder are known from DE-A-36 23 327. The pneumatic cylinder and the striker can be swivellable so that the striker, during impact with the containers, moves along with the latter. This is intended to avoid the striker braking the containers.
A diversion element in the form of a striker operated by a cam is known from DE-C1-37 34 599. A cam segment for driving a striker is known from DE-A-39 17 541.
It is known from DE-C1-38 32 408 to arrange for the pneumatic cylinder to act on a triangular push rod which is rotatable about a housing-fixed pivot and to thereby accelerate an element transmitting the cross impulse.
Disk-shaped self-rotating diversion elements with spiral-shaped diversion segments on the circumference are known from DE-C1-37 22 515. The diversion segments can be comprised of brushes.
With diversion apparatuses, it is always required on the one hand to allow as high a speed of the transport apparatus as possible and on the other hand to divert the items so gently that there is no danger of their falling over. They are also to function reliably even if the items are travelling closely spaced or in immediate succession.
The object of the invention is to make possible higher throughput rates of the items without the items falling over, and to allow small spaces between the items.
This object is achieved according to the invention in that the diversion element carries out a complete extension and retraction movement during a single to-or-fro movement or swing of the drive apparatus.
If the drive apparatus is a pneumatic cylinder for example, and the piston is extended during a diversion process, it retracts again during the next diversion process and vice versa. If the piston is extended or retracted approximately halfway and has practically reached its maximum speed, the diversion finger is located at the end of its swinging out or extension movement. Only the mass of the gear-unit elements need be braked and accelerated again for the return movement. The piston on the other hand maintains its direction of movement and its speed.
An advantage compared with a normal pusher, i.e. a diversion element which is extended by one stroke of the cylinder and retracted again by the other stroke, is that there are no overshoots at the end of the extension movement of the diversion element. A cylinder displays this overshoot at the end of a stroke through the kinetic energy of the masses involved. The overshoot of the piston is transmitted to the diversion element and can lead to the falling over of relatively labile items such as bottles. A further advantage is that the piston is at almost its maximum speed when the diversion element is completely extended. The diversion element therefore travels back extremely rapidly.
The gear unit which transmits the piston movement to the diversion element is preferably a coulisse link mechanism, the coulisse being able to be a straight track with a wave in the centre. The cylinder is arranged in longitudinal direction of the coulisse and the end of the piston rod drives a sliding block or a roller in the coulisse. The movement is transmitted from the sliding block onto a crank lever via a push rod. The push rod lies approximately across the coulisse and the crank lever is swivelled to and fro by it only by approximately 20xc2x0. The free lever arm of the crank lever is the diversion element or the diversion finger. With standard 0.75-1 or 1-1 drinks bottles, a sufficient extension path of approximately 1 cm is produced. The extension or swivelling out movement of the diversion finger can be harmonized very well with the conditions of transport and of the diversion process of drinks bottles. The delay due to the breaking-away of the piston and the high transmission ratio of the coulisse link mechanism lead to an initially relatively slow acceleration. This can be balanced by a corresponding anticipatory control. The diversion finger then gains speed rapidly over the coulisse link mechanism, is braked again when the sliding block is located at the vertex of the wave, and travels back extremely rapidly because the cylinder has then reached its full end speed. In the end position, an overshoot of the cylinder is harmless, as the latter has no effect on the diversion finger because of the high transmission ratio.
The conversion of an extension stroke or a retraction stroke of a cylinder into a complete diversion movement, i.e. the extension movement and the retraction movement of the diversion finger or other diversion element, is also possible by means of a scissors mechanism, a toggle lever or a crank drive.
The cylinder can be arranged vertically downwards, which has the advantage that the structure is very space-saving depthwise. However, it can also be arranged rearwards so that the diversion device is very flat. If the cylinder is arranged downwards, a small difference may result between retraction stroke and extension stroke of the cylinder, as gravity contributes to the downward movement. This can be avoided by providing compressed-air supplies with different pressures for the two directions of travel. Instead of one five-/two-way valve, triggering can be e.g. by two three-/two-way valves via various pressure sources. The control times or the travel time of the cylinder can be further accelerated by not switching over these individual valves in direct sequence, but relieving the cylinder earlier on one side by a premature venting (anticipatory control time) so that the breaking-away process is made easier during start-up.
Furthermore, the travelling speed of the cylinder can be increased by providing the control valves in duplicate and placing them directly onto the cylinder, so that the air ways are kept short. This means that two solenoid valves are placed directly at both one and the other cylinder end, which are triggered simultaneously and ensure an increased supply of compressed air and swifter venting.
Preferably, the crank lever and the diversion finger swivel about a horizontal axis which lies approximately parallel to the direction of transport, and at the same time the end of the diversion finger moves from top to bottom during diversion. This is particularly advantageous because the vertical force component acts favourably on the stability of the bottles; the bottles are so to speak pressed onto the base.
Naturally, the swivelling axis of the diversion finger can also be set in any other direction, e.g. upwards, or with lateral diversion. However, diversion by an upward swivelling of the diversion finger in particular is not so stable and leads to increased falling over of the bottles.
By setting the swivelling axis laterally, i.e. across the direction of transport, the diversion finger imparts an additional speed component in the direction of transport to a bottle during the diversion process.
Preferably, the crank lever is developed such that both lever arms, one of which is connected to the push rod and the other, free lever arm, is the diversion finger, are mounted in rotation-resistant manner on a shaft, at a distance from each other. The whole mechanism comprising cylinder, coulisse, push rod and first lever arm of the crank lever can thereby be encapsulated in a housing. On one side, only the shaft is extended, and the diversion finger is mounted at the end of the shaft. The diversion device can be cleaned easily because of this almost complete encapsulation. This is important in operations in the food industry. On a purely functional level, it would also be possible to drive the diversion finger, not via a shaft but as part of a scissors mechanism. However, the whole mechanism would then lie open and cleaning would be made much more difficult.
In a toggle-lever gear unit, the toggle lever is arranged between a housing-fixed fulcrum and the diversion finger or the crank lever, and the pneumatic cylinder acts on the joint of the toggle lever.
Instead of a pneumatic cylinder, a magnetic coil with movable armature can also be used as drive apparatus travelling to and fro. The armature can be moved to and fro between two magnetic coils, the movement, similar to that of the piston, being transmitted to the diversion element by means of a coulisse or toggle lever.
If a stepped motor swinging to and fro is used as drive apparatus, a crank drive is expediently used for the transmission of the movement.
With the diversion device according to the invention, the strength of the diversion impulse can also be controlled, which makes it possible to knock the containers selectively onto one of two or more conveyors running beside the original conveyor. For this, the control system is designed such that the valves can be supplied from various pressure sources so that the cylinder is optionally operated e.g. at 3 or at 5 bar, which affects the travelling speed of the piston, the extension or swivelling out speed of the diversion element and thus the strength of the diversion impulse and the ejection width of the individual containers.